Means for reducing contact capacitance



May 8, 1956 1 H. REAGAN MEANS FOR REDUCING CONTACT CAPACITANCE FiledJan. 16, 1953 ATTORNEY States,- Patff O t @144;967 g MEANS FOR REDUCNGCONTACT i j CAPACITANCE Leim` III.,-Rag-a'11,` assirgnor, by vniesne',`ass,ignments, tov vGeneral Dynamics Corporation, a corf-pgnvfpeawafinvention relates j*forE reducing Vcontact A s e-linelectricalfcircuitsl t f Y .'Yeryl often electrical `vcircuits includecontacts which llrhir forma Acapacitorwhen open so that'two circuitsareparl tiallyccupledwhen connectionsare broken by the contacts.'Forcxample, in a telephone circuit these contarts may..forrna capacitorwhereby talkingcur'rents are thetalkingzpath of awherebyrachiefoperatormay be connected with a'talking circuit leading-toan operatore-position.-

i As in the case 'ofwmost telephone circuits, the positive batteryEVterminal -is describedv as iconnected" with" ground. For this reason,I refer to the negative pole as battery and the positive pole asgrounded It should be understood that this condition could be reversedor that any other well known power source maybe used without changing myinvention.

Briey, observation relay 120 has contacts 124 and 127 which are in atalking path including conductors TT` and RR, respectively. When open,kthese contacts form a capacitor acrosswhich conversation currents mayow by capacitive coupling. Of course, it isinot possible to predict whencross-talk, electrostatic charges, or the like, may occur with 100%accuracy. This is because many unpredictable factors may enter into theproblem, for example, how loud a person may talk. To avoid thiscapacitance, I provide a second set of contacts 123 and 126 to isolateone plate of the open contact capacitor and contacts 125 and 128 toprovide a ground connection to this plate thereby eliminating anycapacitance coupling tending to interconnect the two ends of conductorsTT and RR. 4

It should be obvious that this relay contact arrangement may be used anytime that `capacity coupling across a. set of open contacts creates aproblem. For example, on occasions a bothersome alternating current suchas cross-talk, for example, or an electrostatic charge may be avoided byusing this arrangement. `The expression draining away electricalcurrents which may result from capacitive coupling is used hereinafterVto describe all of the situations which may arise. It 'should beunderstood to include both'alternating currents, electrostatic charges,and the like, as well as all processes such as those called draining,by-passing, and the like. V

More specifically, my invention shows telephone equipment 105 whichmaybe seized fromoperator position 101 in anysuitable manner such as theinterconnection of plug l102 and jack 103, for example. Thisinterconnection of plug and jack causes the operation of operatorbattery relay 110 over the path extending from grounded f .1-Applicationlanuaryi, 19'55',seria1N0f.s31,6zs .1'0-

2,744,967 s Paten'teitlA May'V 8.,

V(|) through the, upper winding of relay 1'10', resistor R1, conductorOT, the tip connections of 'jack 103 and plug 102 'and transmitter T1,"conductor OT and resistor'ljRZ to (1+) batteryby'wayuof thelowerjwinding of relay 110.", This path ,alsofsupplies battery for vtheoperators transmitter lT15 `Contacts 111 close thereby completing anobvious 'circuit"to light lamp Llfjver couductor'RR as an indicationthatthe operator at position101jha`s .taken psitionIf:another,personLthechief "operator, forl example, wishes'to superviseor"rno`nitor operator position 101, key K1 is thrown `causingobservation relay. 120 tooperate by way of battery, closed vconta'tctsK1,' conductor "-PU; and Ithenpper windin'gfof vrelay 120 to. grounded(+P). This relay may be held directlyffrom key K1 or in some instances alocking path` may be provided independent of the original operatingpath,as required.. In fthis ,case 'relay 1 20 closes'its preliminary or xf'contacts- 122 thereby locking to` grounded (-1-)A orf conductorH,-"su`pplied through contacts K2, when operated.4 Con- 'tact's123 124,126`and"'127operate to complete a talkingfpa'thfrom the chiefoperatorsicircuitlol to position 'circuiti1`0`1r iviafconductors'IT'vand RR.' `Thechief operator"`104 iriay. now vliSLell.' talk'orperformv any necessary supervisoryfunctions after whichl she openscontacts K1 and KZfthereby releasing'v observation relay l1 2'0. Responsivefto the releasefofy observation relay120, contacts1231241f126and 127 op'en tobreak the,path over which the chiefoperatormwasv connected. with operator position 101. *j 'A i If theoperator atfpcs'ition101wishes1to'monitor a1 call, she actuatesvkeyK31tl1erebyoperating` ,'inonitor, y relay",` 130 ','toffop'encontacts 131 nd. leicontacts 132. ,Contacts 13K-open `the `c irct'1itto'trl smitten T1atj the -operatorfs headset, thus preventingan'annoyirrg batteryv click and also disabling transmitter T1 so thatthe operator may not inadvertently be heard by conversing subscribers,such as subscriber A,`for example. At contacts 132, a circuit iscompleted so that when observation relay,120 operator is monitoring. Inthis manner, the chief operoperates to close contacts 121, lamp L2lights if the ator may distinguish between calls where the operatorkposition 101 is giving service and those where she ismerely-listening-in.

Means is providedfor reducing any cross-talk in the circuit leading fromchief operator circuit 104 to position circuit 101 which may result fromcapacitance at the contacts of relay 120. In the past, only one set ofcontacts such as 124 and 127, for example, would serve to 'complete thetalking path,`there being no relay having `duplicate contacts such as123 and 126. In this case, when contacts 124 and 127 are open, acapacitor is formed in each of their gaps whereby a small portion of theconversation currents may be capacitively coupled to conductors'IT andRR therebycreating cross-talk. To avoid this undesirable feature, Iprovide a second set of contacts V123 and 126 in series with contacts124 and 127 thus isolating one plate of` each of the capacitors at "cordcircuit to another through open contacts such as 124 and 127. Myinvention eliminates this type of crosstalk also.

YWhen the operator at position 101 disconnects plug

